The invention relates to a device for transmitting a force in a force-measuring cell with a parallel-guiding mechanism wherein a fixed, stationary parallelogram leg and a movably guided parallelogram leg are connected to each other by parallelogram guides, wherein the stationary parallelogram leg and/or the movably guided parallelogram leg has a part which serves the function of fastening and has at least two fastening portions. Each of the fastening portions has at least one hole running perpendicular to one of the surfaces of the respective parallelogram leg. The holes serve to attach a load carrier to the force-transmitting device and/or to attach the force-transmitting device to a housing or to an intermediate holder. In addition, each of the parallelogram legs has slot-shaped incisions.
The slot-shaped incisions in the fastening part of a parallelogram leg have a stress-uncoupling function, preventing the propagation of a force or stress from one or more fastening portions to the rest of the parallelogram leg and to those parts of the force-measuring cell that serve to receive and transmit the force generated by a load acting on the movably guided parallelogram leg. In the case where this kind of force-measuring cell is used in a scale, the connection of a weighing pan or a weighing-pan support to the vertically movable parallelogram leg, or the connection of the force-measuring cell or in particular of the force-transmitting device to a housing and/or to an intermediate holder is often accomplished by means of screws. This leads to stresses which are caused on the one hand by cutting the tapped holes in the material that the parallel-guiding mechanism is made of, and on the other hand by tightening the screws in the threaded holes. Preferably, the propagation of these stresses to the rest of the force-measuring cell is avoided or at least reduced by slot-shaped incisions or other cutouts in the material of the fastening part of the force-transmitting device. As is commonly known, forces and stresses of this kind which come from the mounting attachment can cause errors in the measuring result.
The state of the art already includes disclosures of force-transmitting devices with slot-shaped incisions or cutouts in the parts that contain one or more fastening portions.
A force-transmitting device of this kind in a force-measuring cell with a parallelogram-shaped guiding mechanism is described in EP 0 511 521. At opposite ends, i.e., in a vertically guided parallelogram leg and a stationary parallelogram leg, this force-transmitting device is equipped with respective fastening arrangements that serve on the one hand to attach a load carrier and on the other hand to attach the load cell itself to a housing. At least one of the fastening arrangements has a fastening portion and a connecting portion that are uncoupled from each other by a transition portion. The latter is formed in the shape of narrow web that is kept as slender as possible, so that the propagation of forces and stresses caused by the fastening means, e.g., by screws, is kept away from the connecting portion. This concept of uncoupling material portions from each other is expressed in the description of EP 0 511 521 B1 through a variety of configurations of the force-transmitting device, in particular in regard to the connecting portion and the fastening portion. In essence, the transition portion is characterized by differently shaped cutouts in the material, in particular circular bore cuts. It is further proposed to arrange ring-shaped grooves around the individual fastening locations in order to uncouple the fastening locations from the rest of the fastening portion.
The manufacturing process for the embodiments proposed in EP 0 511 521 B1 is relatively expensive, particularly in the case of the ring-shaped grooves surrounding a fastening location.
A weighing cell is disclosed in DE 195 35 202 C1 with a parallel-guiding mechanism consisting of a housing-based fixed part and a load-receiving part which are connected by two parallelogram guides. In a first embodiment, the housing-based fixed part has at least two vertically oriented holes to fasten the weighing cell and is equipped with slot-shaped incisions to uncouple the rest of the housing-based fixed part from the area around the fastening holes which is affected by the screws. The incisions in this case consist of one slot-shaped incision each from the top and from the bottom, where the slot-shaped incision from the bottom is extended by an angled-off horizontal portion in which one of the vertical holes ends.
In the second embodiment, at least two horizontally extending holes are provided for fastening the weighing cell to the housing, with the holes ending in slot-shaped incisions entering from the sides. A third slot-shaped incision which runs likewise in the vertical direction is arranged between the holes that run side by side. This configuration leaves only a vertically extending web in place and thus separates the housing-based fixed part from the area around the fastening holes which is affected by the screws, whereby the part of the weighing cell that performs the measuring function is uncoupled from the fastening part in regard to stresses and forces. Common to both embodiments, the horizontally and the vertically directed slot-shaped incisions traverse, respectively, the entire width or the entire height of the force-transmitting device.
This embodiment has the drawback that the structural strength, specifically of the housing-based fixed part and/or of the load-receiving part, suffers as a result of the slot-shaped incisions that run along the entire height or width of the respective parallelogram leg of the force-transmitting device. In particular, this concept no longer leaves the entire height or width of the respective parallelogram leg available to absorb laterally acting torques.